bundles/apt: allow variables {os} and {os_release} in sources.list entries

bundles/apt/items.py

@@ -103,7 +103,10 @@ pkg_apt = {
 for name, data in node.metadata.get('apt', {}).get('repos', {}).items():
     files['/etc/apt/sources.list.d/{}.list'.format(name)] = {
         'content_type': 'mako',
-        'content': "\n".join(data['items']),
+        'content': ("\n".join(sorted(data['items']))).format(
+            os=node.os,
+            os_release=supported_os[node.os][node.os_version[0]],
+        ),
         'triggers': {
             'action:apt_update',
         },